Apparatus for testing potentiometers

ABSTRACT

An apparatus for testing potentiometers utilizing an endless carrier which moves past a plurality of devices positioned at stations along the carrier. A feeder device inserts potentiometers into potentiometer supports on the carrier, an adjusting device moves the slider of the inserted potentiometer to a base position, and an evaluation device moves the slider while simultaneously measuring test parameters of the inserted potentiometer. In one embodiment, an ejection device is included which ejects tested potentiometers into selected receptacles.

United States Patent [191 [4 1 Dec. 3, 1974 Bothner APPARATUS FOR TESTING POTENTIOMETERS [75] lhventorz- Manfred Wolfgang Bothner,

Geretsried, Germany [73] Assignee: Bunker Ramo Corporation, Oak

Brook, Ill.

[22] Filed: Feb. 12, 1973 [21] Appl. No.: 332,008

[30] Foreign Application Priority Data Feb. 17, 1972 Germany 2207525 [52] U.S. Cl. 324/63, 324/73 AT, 324/158 R [51] Int. Cl .t G01! 27/02 {58] Field of Search 324/63, 73 AT, 158 R [56] References Cited UNITED STATES PATENTS 2,840,784 6/1958 Adams 324/63 X 3,160,810 12/1964 Vcrcesi ct all 324/63 7/1969 Dodge ct al. 324/63 Primary ExaminerStanley T. Krawczewicz Attorney, Agent, or FirmDavid R. Bair; F. M. Arbuckle 1 [57] ABSTRACT An apparatus for testing potentiometers utilizing an endless carrier which moves past a plurality of devices positioned at stations along the carrier. A feeder device inserts potentiometers into potentiometer supports on the carrier, an adjusting device moves the slider of the inserted potentiometer to a base position, and an evaluation device moves the slider while simultaneously measuring test parameters of the inserted potentiometer, In one embodiment, an ejection device is included which ejects tested potentiometers into selected receptacles.

17 Claims, 17 Drawing Figures PATENTEW 3,852,665

' sum 02 05 w .FIG. 2

PATENTELBEB' awn 3852.665

saw an ar 10 a q- 9 LL.

' PATENTEL 31974 52 5 i //W J 63 4L rm FIG. 9

PATENIEL w? M SHEET 08 HF 10 FIG.6

PATENIE DEE 3mm sum 07 UF 10 PATENTELUEII 3mm 3,852,665

sum 10m 1 FIG. I30

FIG BC! FIG. |3b

max 5% max 5% FIG. l5e F|G.,l3c A APPARATUS FOR TESTING POTENTIOMETERS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for testing potentiometers, utilizing an. endless carrier having support devices for carrying potentiometers to various test stations of a measuring system.

2. Description of the Prior Art After the production process, potentiometers are usually tested for certain parameters such as continuity, total resistance, and contact noise before they are released for sale. The time required for testing must be short so that the cost of testing does not significantly contribute to the total cost of each potentiometer. The production cost of miniature potentiometers or trimmer potentiometers is very low in modern production technologies, and the cost of testing the potentiometers can have a significant influence on the total cost of the potentiometers. Therefore, a highly automated testing procedure is required to economically test such potentiometers. I

A known system comprises a working table with a rotating disk and a testcabinet connected to the table via cables. The rotating disk is provided with twelve holders on its periphery, so that twelve potentiometers can eters which pass through all test stations without rejection are released for sale. Boththe mechanical equipment and the expensive, so that the cost of production testing utilizing such system is high. Further, the system is prone to .malfunctions because of complexity.

An additional disadvantage of the known system results from the fact that the slider of each potentiometer must be moved several times over the total resistance range in order tomeasure the test parameter. Such movement is required when the continuity of the resistor and the peak noise of the potentiometer are to be measured. The wear resulting from such prior art testing is detrimental, particularly for trimmer potentiometers which are normally adjusted only once to the value required for their operation. Since trimmer potentiometers are notre-adjusted during their entire lifetime, they are of simple design and are easily affected by mechanical loads or stress resulting from such testing.

SUMMARY OF THE INVENTION An object of this invention is to create a reliable and economicaltesting system which can test potentiomelectronic I instruments requiredin such prior art system are very According to the invention, this object is reached by providing an apparatus having an endless carrier which is movable past a plurality of devices positioned at stations adjacent the carrier. The endless carrier has a plurality of potentiometer supports which hold the potentiometers. The devices stationed adjacent the endless carrier operate upon the potentiometers and include: a feeder device for inserting potentiometers into the supports, an adjusting device for moving the slider of the potentiometers to a base position, and an evaluation device for moving the slider through the entire resistance range while simultaneously measuring test parameters of the potentiometer.

The mechanical design and electronic circuitry of the potentiometer test apparatus of this invention is very simple, since several parameters are simultaneously tested in the evaluation device. For example, continuity, contact noise, and total resistance of each potentiometer can be tested inthe evaluation device. Since all the required measurements are made in the evaluation station, a decision can be made immediately after testing in a single station to accept or reject the potentiometer.

The evaluation device is conveniently provided with a cathode-ray tube and a constant-current source which areconnected to the potentiometer in the evaluation station. Potentiometers generally'have three ter-- minal contacts and are referred to hereinas a first terminal Contact, a slider contact, and a second terminal contact. The output terminals of the constant-current source are connected between fthe first terminal contact andthe slider contact of the potentiometer,- while the second terminal contact of the potentiometer and the slider contact are connected to the vertical input of the cathode-ray tube. Several malfunctions of a potentiometer can then be recognized on the pattern displayed on the screen of the cathode-ray tube. When a deflection voltage which depends upon the position of the potentiometerv slider is applied to the horizontal I t resistance linearity do not affect the displayed pattern eters while minimizing wear of the potentiometers during testing.

during rotation of the potentiometer slider.

Potentiometers are frequently provided with'a slip clutch to prevent destruction of the slider when rotational motion causes the slider to exceed the end positions. The slider is frequently'driven by a spindle which engages a member moving the slider. When the slider hits a stop provided at the ends of the resistor body, the

force between the spindle and the member increases.- In order to obtain the slip-clutch effect, the member is of this type canhave a U-shaped brace which enters into the thread grooves of the spindle and is inserted in a plastic block abutting the spindle. When this block is kept in a certain position while the spindle rotates, the block is deformed by the increased force acting upon the spindle, and the brace jumps from one thread groove on the spindle to the next groove.

In potentiometers with circular resistor bodies a known slip clutch provides for a coupling between the slider and a disk, with the disk having radial elevations and grooves engaging the spindle. When a certain driving force is exceeded, the elevations and grooves disengage the spindle until the spindle is moved in an opposite direction.

As has been mentioned above, trimmer potentiometers are usually highly sensitive to mechanical loads, and the slip clutches of trimmer potentiometers are particularly sensitive to mechanical loads. The slipclutch action can be repeated only a few times without serious damage to the trimmer potentiometer. Standards have been proposed requiring that the slip clutch of a trimmer be able to jump (or idle) at least cycles over thread grooves without damage. It is therefore desirable to keep the slip clutch out of operation during the testing procedure to avoid quality losses in trimmer potentiometers. The risk of actuating the slip clutch is particularly great when the slider is brought into a certain basic position in the adjustment station of the test unit. For practical considerations, the basic position is selected so that the slider bears against one end of the resistor body. However, this is usually the range in which the slip clutch begins to become effective when the slider is rotated.

lt is advantageous to adjust the potentiometer to a certain basic position by moving the potentiometer slider toward one of the terminals until the ratio of the total resistance between the terminals to the resistance between the slider and the terminal selected has reached a certain value. Naturally, this value must be below the point at which the slip clutch is normally actuated so that the basic position can be reached without actuating the slip clutch. The apparatus of this invention can be used wherever the slider of a potentiometer or trimmer potentiometer must be adjusted to a certain resistance value.

It is advantageous to establish the ratio of the total resistance between the terminals to the resistance between the slider and one of the terminals by comparing voltages. To do this, the end terminal contacts of the potentiometer to be tested are connected to a constantvoltage source, and the voltage between the potentiometer slider contact and one of the terminal contacts is compared with a reference voltage by means of a differential amplifier. A circuit of this type is simple, can be produced at low cost, and operates with high accuracy. Moreover, the desired voltage ratio can be easily adjusted.

It is desirable to run the slider once completely over the entire resistor in forward and backward directions while the potentiometer is in the adjustment station, where the basic potentiometer position is determined. Full backward and forward rotation of the slider ensures removal of oxide layers and dirt films from the resistor, but does'not affect the ensuing potentiometer testing.

In a preferred embodiment, an ejection station is provided after the evaluation station. In the ejection station the tested potentiometers are released and sorted. In principle, the tested potentiometers could be ejected in the evaluation station. However, since the evaluation station is the station in which the potentiometers remain for an extended period of time, it is more advantageous to provide a separate station and ejection device for potentiometer ejection. The cycle time (the time the potentiometer is in the test unit) is then reduced.

It is also advantageous to provide several keys and collecting receptacles for each key and to mount a sorting mechanism between the ejection device and the collecting receptacle. The sorting mechanism takes care of the transport of the released potentiometers to a collecting receptacle when a corresponding key is depressed. In the simplest case, two such collecting receptacles are used, one for receiving the accepted potentiometers and the other for receiving potentiometers having defects of some kind. It is advantageous to provide several collecting receptacles for defective potentiometers, with one receptacle provided for each type of potentiometer malfunction. The malfunctions which occur most frequently can then be readily determined, and the production process modified to minimize the number of defects.

When collecting receptacles are used, it is desirable to provide each receptacle with a counter for counting the potentiometers entering into the particular receptacle.

The carrier may be provided in the form of a wheel. This simplifies the design'of the testing unit.

In a preferred embodiment, the wheel of the carrier comprises a square base which is mounted on a shaft and carries exchangeable potentiometer supports on its radial faces. The test set can be rapidly adjusted from one type of potentiometer to be tested to another type with different dimensions by inserting an appropriate potentiometer support.

In one embodiment, the potentiometer support comprises a clamping device. The clamp is of a very simple design, and the potentiometer to be tested is simply pushed into the clamp at the feeder station.

In a preferred embodiment, the carrier wheel is provided with a self-locking Geneva drive (for converting continuous motor drive to station-cycle operation).

This ensures, in a simple fashion, that the carrier wheel is always rotated the same angle.

Further, each potentiometer support is conveniently provided with a group of three contacts which are connected to the three terminal contacts of the potentiometer inserted into the support. Contact isestablished while the potentiometer is mechanically supported, and no additional operation must be performed 'in order to establish electric contact. Each contact group moves from one test station to the next as the carrier rotates, whereby each contact group is connected to the corresponding measuring equipment of the test station.

It is advantageous to connect the shaft of the feed wheel to a set of mercury transfer couplers to establish connections between stationary terminals and the contacts of the potentiometer supports rotating with the feed wheel. It is possible, in principle, to connect each potentiometer to be tested in each test station to stationary contacts (contacts which do not rotate with the carrier wheel). However, the disadvantage of this configuration results from the fact that the measurements to be taken are affected by the greatly varying contact resistances. This is not the case, when mercury transfer couplers are used.

' A switching-means may be provided on the shaft of the carrier wheel. This switching means establishes a connection between the contacts on the carrier wheel and the measuring equipment as required by position of the contacts in each station. By coupling the switchingmeans to the shaft of the carrier wheel, a certain switch combination is selected ineach position of the shaftcorresponding' to the potentiometers to be tested at each particular test station. The switch combination ensures that the measuring equipment terminals pertaining to a certain test station are connected with the contact groups located at the particular test stations in which measurements are taken. A switching device of this type can be easily built and is very reliable in its operation.

' Such a switching means may be built from magnets and reed contacts. Either the magnets or the reed contacts are mounted on a disk which is connected to the shaft driving the feed wheel. Respective reed contacts or magnets are fixedly mounted on a stationary coaxial cylinder surface. The magnets and reed contacts are arranged so that in each position of the shaft, a certain combination of reed contacts is closed. A switching means of this type is very reliable in its operation and can be produced at low cost.

A feed duct may be provided at the feeder station. One potentiometer at a time can be transferred by means of a transfer device from the feed duct to a potentiometer'support on the feed wheel. When a feed duct is provided, the operator of the test unit need not The feeder device may be providedwith a spindle device whichacts upon'the potentiometer to be moved. This simplifies the design of the feeder device and ensures an accurately controllable transfer motion of the potentiometer.

Further, the slider driving units in the adjustment and evaluation devices may be provided with limiting switches which interrupt the slider motion after a certain adjustable rotationof the driving units, or after a certain number of full rotations in a particular direction of motion. The potentiometer slider may then be moved automatically over the full resistance range without need' for a manual interruption of the driving force or a manual reversal of the direction of rotation. Additionally, the limiting switches ensure that the slider, once it has been moved from a previously adjusted basic position, can approach the end points of the resistor'only to the extent where a mechanical overload cannot occur and the slip clutch is not actuated.

It is advantageous to provide means which permit the limiting switches to return to their initial positions regardless of the position of the driver shaft. The shaft of the driving unit need not be rotated in order to return the limiting switches to their initial positions. In some cases, the potentiometer to be tested may be removed from the evaluation device when the potentiometer slider is not in the baseposition. In such instances, before anew potentiometer is introduced, the limiting slider of the potentiometers;

switch must be returned to its initial position to prevent excessive rotation of the potentiometer.

The limiting switch is conveniently provided with a rotatable disk which is rotated either directly by the driving shaft or via a reduction gear. The disk can move between two positions of rotation which are determinedby the position of photoelectric transmission units. A rotating disk which is rotated directly by the shaft of the driving unit is used only when the shaft of the driving unit has to perform a maximum of one rotation for rotating the potentiometer slider. Such is the case with potentiometers having a circular resistor body with a slider in concentric position. When testing potentiometers having a slider driven by a worm gear, a reduction gear is inserted between the driving shaft and the rotating disk. In any event, the rotating disk must rotate less than 360 when the slider is moved over the entire resistance range. A limiting switch comprising a rotating disk with photoelectric transmission units can be easily produced and ensures highly accurate measurements.

An electromagnetic clutch may be inserted between the rotating disk and the shaft of the driving unit, and the rotating disk may be biased by means of a spring so that the disk returns to its initial position when the clutch is released. In this way, the return of the rotating disk to its initial position can be easily initiated via an electric contact.

Moreover, the photoelectric transmission unit may be adjustable to set the limiting positions of the rotating disk. Then the limiting switch can be adjusted to various types of potentiometers to be tested for which various angles or various numbers of full rotations are required. I

One of the separate, but similar, driving units is conveniently used in each of the adjustment and evaluation devices.

It is advantageous to use a slider-actuating member mounted on the driver shaft and shiftable in the axialdirection. With such an actuating member, the entire driving unit does not have to be moved in axial direction when the actuating member is disengaged and removed from the potentiometer. A solenoid can be used to shift the actuating member against the force of a compression spring to facilitate electrical control of the advance of the actuating member in axial direction.

BRIEF DESCRIPTION OF THE DRAWINGS The following description of the invention refers to a particular embodiment shown in the following drawings: a

FIG. 1 is an overall view of the test apparatus of the invention;

FIG. 2 is a front view of the carrier wheel, the feed duct, and the feeder device of the test apparatus of.

FIG. 1;

FIG. 3 is a top view of the driving mechanism in the test apparatus;

FIG. 4 is a cross section taken along line 4-4 of FIG. 3;

FIG. 5 isa cross section taken along line 5-5 of FIG.

FIG. 6 is a cross section of the carrier wheel;

FIG. 7 is a side view of the. driving unit for driving the FIG. 8 is a top view of the driving unit of FIG. 7;

FIG. 9 is a cross section taken along line 99 of FIG. 8;

FIG. 10 is a cross section taken along line 1010 of FIG. 8;

FIG. 11 is a schematic diagram of the voltagecomparison circuit;

FIG. 12 is a schematic diagram of the circuit for measuring the test parameters; and

FIGS. 13a through 13e are typical oscilloscope test patterns.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I shows a work bench with a test apparatus of the invention. The test apparatus is mounted on a rack in cabinet 1. The apparatus comprises three units which can be mounted in racks. The lowermost unit comprises the mechanical components 2 which feed the potentiometers to be tested to the various test stations. The unit in the center comprises several subunits with the electronic control and test equipment 3. The uppermost unit contains an oscilloscope 4. Test cabinet 1 is placed on bench S in which a keyboard 6 is inserted. Several collecting receptacles are mounted under the top of bench 5. These receptacles are filled with tested potentiometers. A slot 8 is provided in bench underneath the ejection area of mechanical components 2 of the apparatus. The ejected potentiometers pass through slot 8 in the bench top into collecting receptacles 7.

Mechanical components 2 comprise: a carrier wheel 9 which acts as an endless carrier; a feed duct and a feeder device 11, both at a feeder station 12; and two driving units 13, which are offset 90 and are used' to drive the sliders of the potentiometers to be tested.

As shown in FIG. 6, carrier wheel 9 comprises a square base 14 having four segment-shaped potentiometer supports 15 mounted on the periphery by means of two screws 16 and 16. Each support 15 carries a clamp 17 which can be used to support a trimmer or potentiometer l8. Clamp 17 consists of a clamping lever 22 which is moved around shaft 21 toward stop by means of a compression spring. That portion of clamping lever 22, which faces potentiometer 18, is rounded so that the potentiometer can be inserted into clamp 17 without need for actuating the clamping lever. The clamping lever is provided with a bore through which a screw 23 passes which, in turn, is screwed into support 15. This screw can be used to adjust the minimum distance between clamping lever 22 and stop 20. Further, each support 15 is provided with three blade contacts 24. A set of three blade contacts 24 is shown in FIG. 3. Blade contacts 24 establish an electric connection to one of each of the terminal contacts 18' of the potentiometer. As shown in the upper portion of FIG. 6, leads 25 are connected to blade contacts 24.

Leads 25 are connected via a plug connector 26 mounted in holding device 15 to a IZ-terminal mercury transfer coupler 27 (shown in FIG. 3) for transferring the measuring currents from the rotating supports to the stationary electrical instruments.

} As shown in FIG. 3, the center of carrier wheel 9 is coupled to shaft 28 which is supported by two ball bearings 29 in front plate 2a of the housing. A Geneva wheel 30 is mounted on the shaft in order to drive the shaft. As can be inferred from FIGS. 3 and 4, the Geneva wheel is driven by a motor 31 via a worm gear 32. Motor 31 is of the disk-rotor type.

Feed station 12 consists of feed duct 10 and feeder device 11, and serves to introduce potentiometers 18 to be tested into supports 15 of carrier wheel 9. Details of feed station 12 are shown in FIGS. 2 and 3. Feed duct 10 is in a generally vertical position and forms a tangent to carrier wheel 9. As shown in FIG. 3, the interior profile of feed duct 10 is such that potentiometers 18 can be introduced only when they are in a certain position. At its lower end, feed duct 10 is provided with an opening 33 facing carrier wheel 9. Potentiometers are transported from opening 33 into holding device 15 of carrier wheel 9 by means of feeder device 11. Feeder device 11 comprises two feed pins 34, which can move radially (with respect to carrier wheel 9) into feed duct 10 and engage the lowermost potentiometer in feed duct 10. Feed pins 34 are mounted on a sliding member 35 which is provided with a thread and is set into reciprocating motion by a spindle 37 driven by a motor 36. A limiting pin 38, which reciprocates between two stops 39 and 40 is mounted on sliding member 35 and extends perpendicular to the direction of motion of the sliding member. Electric switch contacts attached to stops 39 and 40 form limiting switches for the motion of motor 36. Motor 36 is conveniently coupled to a device which shuts off the motor once a torque exceeding a certain critical value is reached. Excessive torque could arise when a potentiometer to be tested jams while it is introduced in the test apparatus.

Two driving units 50 and 51 are mounted in two test stations in offset relationship and are used to rotate the sliders f0 potentiometers 18. FIGS. 7 through 10 show details of the driving units. FIG. 3 shows the support of one of the driving units. Driving units 50 and 51 are designed for driving potentiometers having a spindle for moving the slider. In order to move the slider from one end of the resistor body to the other end, several spindle rotations are required. The driving unit shown is provided with a driving motor 52 which is a disk-rotor motor like the driving motor of carrier wheel 9.

Driving motor 52 is coupled to one end of a shaft 53. The other end of shaft 53 is carried in a sleeve 54 which in turn is carried within a second sleeve 56. Sleeve 56 is driven from shaft 53 by a cross-pin 53'. Shaft 53 is supported in bearings 55, and sleeve 56 in bearings 55'. The intermediate sleeve 54 has axially elongated slots 57 through which the cross-pin 53' passes, so that the sleeve 54 is driven thereby in accordance with the rotation of shaft 53, but can slide longitudinally thereon, and inside of sleeve 56. The inner end of the sleeve 54 is provided with a radial flange 58. A compression spring 58 acts on one side of the flange, normally keeping the sleeve 54 in extended position. A yoke 59 carrying ball bearings 60 is mounted on a rotary actuator magnet 61 (FIG. 7) with the bearings 60 engageable with flange 58, so that when the magnet 61 is energized, the flange 58 and sleeve 54 are retracted against the force exerted by spring 58'.

The front end of sleeve 54 is provided with a driver head 54, carrying a screwdriver tip 54", formed so that it enters into the screw groove usually provided on a potentiometer with a spindle for moving the slider. The tip 54" is removable (see FIG. 10) so that different types can be used as may be necessary for different forms or sizes of potentiometer spindles. A worm gear 62, which can be used to drive a gear 63, mounted in the housing of the driving unit, is mounted in line with shaft 53. Gear 63 is mounted on a shaft 64 which carries a rotatable disk 65. Disk 65 is provided with a radial slot 66. As can be inferred from FIGS. 7 and-9, two photoelectric units 67 and 67 are mounted so that anincandescent lamp 68 is situated on one side of the disk and a photoelectric pickup 69 is situated on the other side of the disk. Light can shine upon photoelectric pickup 69 only when slot 66 or rotating disk 65 is situated adjacent photoelectric pickup 69. One of the two photoelectric units 67 can be rotated around shaft 64 in order to adjust the angular distance between the two transmission devices.

Rotating disk 65 is not directly coupled to gear 63, but an electric clutch 70 is inserted between the rotating disk and gear 63. Further, rotating disk 65 is mewhen carrier wheel 9 is rotated.

chanically biased by a spiral spring 71 so that rotating I 36, and 52, electric clutch 70, and the photoelectric transmission devices 67 on the one hand, and electronic control and measuring units, on the other.

As shown in FIG. 3, disc 80 is mounted on shaft 28 which drives carrier wheel 9. Disk 80 is subdivided into four adjacent annular sections on its periphery. In one sector of each ring space, there can'be inserted a permanent magnet 81, six of which are shown in the figure. As shown in FIG. 5, disk 80 is surrounded by a supporting member 82 on which reed contacts 83 are mounted. Reed contacts '83 are arranged so that they can be actuated by permanent magnet 81. By providing supporting member 82 with reed contacts 83 and disc 80 with permanent magnets 81, a certain combination of re'edfcontacts is closed in eachof the four rotational positions of shaft 28. In this fashion, characteristic switching positions are obtained for each of the four rotational positions. Reed contacts 83 form part of the circuitry so that blade contacts 24 of carrier wheel 9 are connected to that, part of the measuring equipment,

whichis cooperatingwith the particular station to which bladecontacts 24 establish connections.

The'following is a description of the operation of the testapparatus of the invention.

Carrierwheel 9 is provided with four clamps which are symmetrically distributed over the periphery of the carrier wheel. Geneva wheel drive 30 effects a 90 rotation of the carrier wheel in the direction of arrow 84shown in FIG. 2. Thus, each clamp 15 passes in succession through feed station I, adjustment station ll, test station III, and ejection station IV. Potentiometers 18 stored in feed duct 10 are in succession inserted into clamps 15 of carrier wheel 9 at the feed station. The feed duct can be supplied with the potentiom- I etersby means of a conventional vibrating device.

-When the carrier'whe'el9 is filled with potentiometers by the'feed station, terminal contacts 18, of each ometers l8 situatedin carrier wheel 9 is therefore connected to one of the twelve contacts of the mercury,

The following adjustments are made on potentiometer 18 in adjustment station II. The slider is moved into a well-defined basic position, i,e., the slider is moved to one end of the resistor body. This is done while voltage comparison measurements are made, as described below with reference to the circuit scheme shown in FIG. 11. The three terminal contacts of the potentiometer 18 are denoted by a, b, and c, with c denoting the slider contact. A constant-voltage source U is connected to contacts b and c. A calibrating potentiometer 18a is connected in parallel to potentiometer 18. The sliders of the two otentiometers are connected to a differential amplifier D which can actuate electric clutch 70. By adjusting the slider of calibrating potentiometer 18a, the desired comparison voltage for v adjusting the principal position is reached. Once the principal position has been reached, electric clutch is actuated so that rotating disk 65 engages gear 63.

As far as the mechanical process of determining the zero point is concerned, screwdriver tip 54 is kept in the depressed position until the current to the rotating magnet is interrupted. This results in a signal which initiates the search for the zero point. When this condition has been reached,-front end 54' of screwdriver tip 54 enters into the'screw groove on the spindle of potentiometer l8.

Immediately after theabove-described zero-point determination, a full backward and forward'run of the potentiometer slider is made in adjustment station II. No

electric parameters are'tested during this backward and forward run. The purpose of this motion of the slider is to rub off any oxide layer or dust particles which may have accumulated on the resistor. During the backward andforward run, electric clutch 7 0 of driving unit 50 remains engaged so that rotating disk 65 is moved along with the slider of potentiometer 18. The angular distance of the two'photoelectric units transmission devices 67 and 67 is adjusted so that slot 66 of disc 65 appears in the field of view of photoelectric unit 67 when the potentiometer slider has reached the'other end of the resistor. In this position, photoelectric pickup 69 of photoelectric unit 67"supplies a signal which is used in the control unit to reverse the rotation of motion of motor 52. The slider is returned to the initial position which is established by a signal supplied by evaluation station III. In evaluation station III, potentiometer 18 is connected to a constant-current source .I and to oscilloscope 4 by means of blade contacts 24, leads 25, and the mercury, transfer coupler 27. FIG. 12 shows the schematic circuit in which potentiometer 18 is connected to the constant-current source I and to oscilloscope 4. The two terminal contacts of the potentiometer are denoted bye and b, and the slider contact is denoted by c. Constant-current source .I is connected to contacts a and c of potentiometer 18. The vertical deflection plates of oscilloscope 4 are connected to contaxts b and c of potentiometer l8, and the horizontal deflection plates are connected to contacts a and c. in the case of wire-wound potentiometers, the output current of constant-current source J typically amounts to approximately 1 mA.

Immediately after potentiometer 18 has entered into evaluation station lll, screwdriver tip 54 of driving unit 51 is in the depressed position. Since the two driving units 50 and 51 are identical in design, their components are denoted by equal reference symbols for the sake of brevity. Rotating magnet 61 is de-energized, whereupon screwdriver tip 54 assumes the protruded position and engages the rotating shaft of potentiometer 18. Electromagnetic clutch 70 is actuated at the same time, so that rotating disc 65 is coupled to screwdriver tip 54. By rotating tip 54, the slider of potentiometer 18 is moved from one end of the resistor body to the other. During this motion, current flows through potentiometer 18, since the potentiometer is connected to constant-current source J.

Typical patterns, some of which are shown in FIGS. 13a through 136, appear on the display screen of the oscilloscope during potentiometer testing. As can be inferred from the figures, the oscilloscope is adjusted so that an ideal total resistance of the potentiometer covers the entire width of the calibrated oscilloscopescreen section. An ideal wire potentiometer results in a straight line which covers the entire width of the oscilloscope screen. FIGS. 13a through 13d show typical test patterns which were obtained with defective wirewound potentiometers. In FIG. 13a, the straight line is interrupted by a pulse which indicates that one point of the resistor is defective and causes noise. The end of the line is not reached in FIG. 13b, which means that the total resistance of the potentiometer is too small. H0. 130 is the typical pattern which is obtained when one of the potentiometer contacts (denoted by a and b) does not coincide with the end of the resistor. The pattern of FIG. 13d is observed, when the resistor is interrupted. Since the noise produced by film potentiometers is much greater than the noise of wire-wound potentiometers, different test criteria must be used with film potentiometers. FIG. 13:: is a typical test pattern obtained with a film potentiometer whose parameters are still within the tolerance limits. The pattern is characterized by large noise peaks which reach their maximum values at the ends of the resistance film. A typical test criterion is that the noise peaks at the ends of the resistance film must be situated within an interval which does not deviate more than percent from the total resistance. ln the rest of the screen area, the noise voltage must not pass beyond the dashed line.

The forward and backward motion of slider c of potentiometer 18 can be repeated if the observer wishes to select a certain portion of the pattern to check a questionable malfunction which occurred in a particular range of the resistor.

The motion of slider c of potentiometer 18 is limited in both directions by rotating disk 65 and photoelectric units 67, 67, as has been described in relation to adjustment station ll. lt is therefore not possible to move slider 0 beyond the ends of the resistor, because driving motor 52 is reversed when one of the photoelectric units supplies a signal. Electromagnetic clutch 70 remains actuated as long as potentiometer 18 resides in evaluation station Ill.

Once the operator of the test apparatus has decided into which collecting receptacle 7 the potentiometer tested should be released, the operator depresses the corresponding key in keyfield 6 of bench 5. After that, carrier wheel 9 rotates in the direction of arrow 84. Consequently, the potentiometer tested is transferred into ejection station IV, and the potentiometer is ejected. For the ejection, clamp 22 is rotated around shaft 21 and against the force exerted by spring 19.

After potentiometer 18 has passed through evaluation station lll, rotating disk 65 of the driving unit 51 cooperating with evaluation station III is briefly disengaged from screwdriver tip 54 so that the driving unit is in its initial or null position during the arrival of another potentiometer for testing.

Since there are always at least three, and at most four, potentiometers in the carrier wheel, the various test operations can be performed at the same time on various potentiometers. The cycle time of testing is determined by the time interval during which each potentiometer is retained in evaluation station lll. Testing in evaluation station Ill requires more time than testing in any other station, because slider c of potentiometer 18 is relatively slowly moved in test station "I. Consequently, circuits which prevent carrier wheel 9 from being rotated before all test operations have been performed are not required. In order to rotate carrier wheel 9 by 90, it suffices to provide a key, e.g., a foot switch, which is depressed by the operator as soon as testing in evaluation station III has been completed.

From the foregoing, it can be readily realized that this invention can assume various embodiments. Thus, it is to be understood that the invention is not limited to the specific embodiments described herein, but is to be limited only by the appended claims.

What is claimed is:

1. An apparatus for testing potentiometers having a resistor element with two end terminals and a slider contact which traverses said resistor in response to rotation of a spindle, comprising a carrier having a plurality of potentiometer supports at spaced points thereon, and a plurality of devices positioned at stations adjacent to said carrier, said carrier being movable to locate each support successivelyat said stations in a predetermined sequence, wherein the improvement comprises an adjusting device at one of said stations including rotary driving means engageable with the spindle of a potentiometer in a support on said carrier adjacent to said one station,

means applying a constant potential to the end terminals of said potentiometer,

means sensing the potential appearing between the slider contact and one end terminal, and

means disengaging said driving means from said spindle when the ratio between the potential across the end terminals of said potentiometer to the potential between the slider contact and said one end terminal has a predetermined value, and

an evaluation device at a subsequent one of said stations, including second rotary driving means engageable with the spindle of a potentiometer in a support on said car,- rier adjacent to said subsequent station,

' oscilloscope has its horizontal deflection input connected to said last mentioned one end terminal and to said slider contact.

4. An apparatus as claimed in claim 1, wherein said evaluation device includes rotation limiting switches, and adjustable actuating means therefor, driven by said second driving means said limiting switches preventing further rotation of said second driving means and said spindle in a given direction when points adjacent the ends of said resistor predetermined by adjustment of said actuating means are reached by the slider contact.

5. The apparatus as claimed in claim 1, wherein said second rotary driving means includes a driver shaft,

and a shaft tip portion adapted to fit a potentiometer spindle,'said shaft tip portion being shiftable in axial direction,

6. The apparatus as claimed in claim 5, wherein said second rotary driving means includes a spring biasing said shaft tip portion toward a potentiometer spindle, and an actuator operable to shift said shaft tip portion away from a potentiometer spindle.

7. The apparatus as claimed in claim 1, wherein said carrier comprises a rotatable wheel.

8. The apparatus as claimed in claim 7, wherein said wheel comprises a square base rotatably mounted on a centrally-positioned shaft, said potentiometer supports being exchangeably mounted on the peripheral faces of said base.

9. The apparatus as claimed in claim 1, wherein each of said potentiometer supports includes three contacts arranged to electrically engage the three contacts of an inserted potentiometer.

10. The apparatus as claimed in claim 1', wherein said potentiometer supports comprise clamps. I

11.,The apparatus as claimed in claim 7, including a self-locking Geneva wheel drive for rotating said rotatable wheel.

12. The apparatus as claimed in claim 8, including a mercury transfer coupler joined to said shaft, said mer cury transfer coupler electrically coupling the contacts of an inserted potentiometer which rotates with said shaft to stationary terminals.

two positions between which said disk rotates.

14. The apparatus as claimed in claim 13, including: an electromagnetically actuated clutch coupling said second driving means to said rotating disk, and a spring biasing said disk so that said disk returns to a predetermined initial position when said clutch is released.

15. The apparatus as claimed in claim 14, wherein said photoelectric transmission units are adjustable for selectively predetermining said two positions.

16. An apparatus for testing potentiometers having a resistor element with two end terminals and a slider contact which traverses said resistor in response to rotation of a spindle, comprising a rotating carrier having a plurality of potentiometer supports spaced around the periphery thereof, and a plurality of devices positioned at stations adjacent to said carrier, said carrier being movable to locate each support successively at said stations in a predetermined sequence, wherein the improvement comprises a feeder device at a first one in sequence of said stations comprising a vertically extending feed duct adapted to receive a stack of potentiometers, the interior profile of said duct being such that potentiometers can be introduced only when they are in a predetermined position, said duct having its lower portion adjacent to said carrier and having an opening therein facing said carrier, and I a feeder device movable radially with respect to said carrier and engageable with the'lowermost potentiometer in said feed duct to move said lowermost potentiometer through said opening into a potentiometer support on said carrier, Q rotary driving means at a second one of said stations engageable with the spindle of a potentiometer carried in a support on said carrier when said support is adjacent to said second station, adjustable control means disengaging said driving means from the spindle of a potentiometer being driven at said second station when its slider contact reaches a predetermined position adjacent to one end of said resistor element, and

' second rotary driving means at a third one of said stations, engageable with the spindle of a potentiometer carried in a support on said carrier when said support is adjacent to said third station, and

second control means sequentially actuating said second driving means to engage the spindle, drive the associated slider contact from the starting point to a predetermined point adjacent to the opposite end of the resistor element, reverse the direction of drive, and return the slider contact to the'starting point.

17. The apparatus as claimed in claim 16, including a motor operatively coupled to said feeder device, and two adjustable stop switches electrically joined to said motor and actuated by the motion of said feeder device to limit the range of movement thereof. 

1. An apparatus for testing potentiometers having a resistor element with two end terminals and a slider contact which traverses said resistor in response to rotation of a spindle, comprising a carrier having a plurality of potentiometer supports at spaced points thereon, and a plurality of devices positioned at stations adjacent to said carrier, said carrier being movable to locate each support successively at said stations in a predetermined sequence, wherein the improvement comprises an adjusting device at one of said stations including rotary driving means engageable with the spindle of a potentiometer in a support on said carrier adjacent to said one station, means applying a constant potential to the end terminals of said potentiometer, means sensing the potential appearing between the slider contact and one end terminal, and means disengaging said driving means from said spindle when the ratio between the potential across the end terminals of said potentiometer to the potential between the slider contact and said one end terminal has a predetermined value, and an evaluation device at a subsequent one of said stations, including second rotary driving means engageable with the spindle of a potentiometer in a support on said carrier adjacent to said subsequent station, means passing a constant current from one end terminal of said potentiometer through the slider contact thereof, and means visibly displaying the magnitude of the potential between said last mentioned slider contact and the other end terminal.
 2. An apparatus as claimed in claim 1, wherein said means visibly displaying the magnitude of potential is an oscilloscope having its vertical deflection input connected to said last mentioned slider contact and other end terminal.
 3. An apparatus as claimed in claim 2, wherein said oscilloscope has its horizontal deflection input connected to said last mentioned one end terminal and to said slider contact.
 4. An apparatus as claimed in claim 1, wherein said evaluation device includes rotation limiting switches, and adjustable actuating means therefor, driven by said second driving means said limiting switches preventing further rotation of said second driving means and said spindle in a given direction when points adjacent the ends of said resistor predetermined by adjustment of said actuating means are reached by the slider contact.
 5. The apparatus as claimed in claim 1, wherein said second rotary driving means includes a driver shaft, and a shaft tip portion adapted to fit a potentiometer spindle, said shaft tip portion being shiftable in axial direction.
 6. The apparatus as claimed in claim 5, wherein said second rotary driving means includes a spring biasing said shaft tip portion toward a potentiometer spindle, and an actuator operable to shift said shaft tip portion away from a potentiometer spindle.
 7. The apparatus as claimed in claim 1, wherein said carrier comprises a rotatable wheel.
 8. The apparatus as claimed in claim 7, wherein said wheEl comprises a square base rotatably mounted on a centrally-positioned shaft, said potentiometer supports being exchangeably mounted on the peripheral faces of said base.
 9. The apparatus as claimed in claim 1, wherein each of said potentiometer supports includes three contacts arranged to electrically engage the three contacts of an inserted potentiometer.
 10. The apparatus as claimed in claim 1, wherein said potentiometer supports comprise clamps.
 11. The apparatus as claimed in claim 7, including a self-locking Geneva wheel drive for rotating said rotatable wheel.
 12. The apparatus as claimed in claim 8, including a mercury transfer coupler joined to said shaft, said mercury transfer coupler electrically coupling the contacts of an inserted potentiometer which rotates with said shaft to stationary terminals.
 13. The apparatus as claimed in claim 4, wherein said limiting switches include a rotating disk driven by said second driving means, and photoelectric units operatively coupled to said rotating disk at points defining two positions between which said disk rotates.
 14. The apparatus as claimed in claim 13, including: an electromagnetically actuated clutch coupling said second driving means to said rotating disk, and a spring biasing said disk so that said disk returns to a predetermined initial position when said clutch is released.
 15. The apparatus as claimed in claim 14, wherein said photoelectric transmission units are adjustable for selectively predetermining said two positions.
 16. An apparatus for testing potentiometers having a resistor element with two end terminals and a slider contact which traverses said resistor in response to rotation of a spindle, comprising a rotating carrier having a plurality of potentiometer supports spaced around the periphery thereof, and a plurality of devices positioned at stations adjacent to said carrier, said carrier being movable to locate each support successively at said stations in a predetermined sequence, wherein the improvement comprises a feeder device at a first one in sequence of said stations comprising a vertically extending feed duct adapted to receive a stack of potentiometers, the interior profile of said duct being such that potentiometers can be introduced only when they are in a predetermined position, said duct having its lower portion adjacent to said carrier and having an opening therein facing said carrier, and a feeder device movable radially with respect to said carrier and engageable with the lowermost potentiometer in said feed duct to move said lowermost potentiometer through said opening into a potentiometer support on said carrier, rotary driving means at a second one of said stations engageable with the spindle of a potentiometer carried in a support on said carrier when said support is adjacent to said second station, adjustable control means disengaging said driving means from the spindle of a potentiometer being driven at said second station when its slider contact reaches a predetermined position adjacent to one end of said resistor element, and second rotary driving means at a third one of said stations, engageable with the spindle of a potentiometer carried in a support on said carrier when said support is adjacent to said third station, and second control means sequentially actuating said second driving means to engage the spindle, drive the associated slider contact from the starting point to a predetermined point adjacent to the opposite end of the resistor element, reverse the direction of drive, and return the slider contact to the starting point.
 17. The apparatus as claimed in claim 16, including a motor operatively coupled to said feeder device, and two adjustable stop switches electrically joined to said motor and actuated by the motion of said feeder device to limit the range of movement thereof. 